Lokrum Island, Dubrovnik, Croatia

Lokrum is an island in the Adriatic Sea 600 metres (1,969
feet) from the city of Dubrovnik, Croatia. It stretches from northwest to
southeast and receives regular ferry service from the city.

Austrian archduke (and short-lived Emperor of Mexico)
Maximilian once had a holiday home on the island. A monastery and a botanical
garden survive from his era. On the island's highest point at 96 metres (315
feet) above sea level stands Fort Royal Castle, which was built by the French,
though it was later named "Maximilian's Tower" by the Austrians. Sources